1. Field of the Invention
The present invention pertains to refining petroleum residues and sludges, and, in particular, to a process for significantly decreasing processing time, reducing capital cost, increasing yield, improving quality and enhancing refining processes by making them safer.
2. Description of Prior Arts
Huge volumes of petroleum residues and sludges are generated by the oil refineries, petroleum shippers and big users of petroleum and petroleum products. Some examples of petroleum residues are the reduced crude such as short or long residues obtained from crude oil atmospheric or vacuum distillation column, respectively; bottom product of used oil re-refinery using either vacuum applied wipe-film or thin film evaporator. Some examples of petroleum sludges are those obtained from the storage tanks of crude oil, fuel oil number 6 or bunker C, asphalt, slop oil and mixture of any two or more of these sludges.
Prior art processes to produce asphalt and other petroleum products from petroleum crude oil residues include straight reduction of crude oil, propane deasphalting of reduced crude and thermal cracking process.
Straight reduction of crude oil needs two-stage process, an atmospheric distillation column is used first to "top" the crude oil followed by a vacuum distillation unit to process the reduced crude to asphaltic residue and other petroleum products. The two (2) stage process is applicable to crude containing 15-30% asphalt. The asphaltic mixture thus obtained consists mostly of asphaltenes and viscous oil which need further processing using techniques such as propane deasphalting to obtain high quality asphalt of penetration number 60-100 useful as paving asphalt.
Thermal cracking is generally done by heating the oil to 480-610.degree. C. under pressure up to 200 psig. This high pressure and temperature process will crack most of the feed oil and will result in a very low yield of asphalt having low viscosity and high penetration number and is therefore not suitable as paving asphalt for roads and highways.
The overhead products produced thus consist mostly of cracked distillate and light ends which are of lesser commercial value than the oil and wax. In addition, the high pressure, high temperature process entails higher capital cost for equipment.
Propane deasphalting is by far the most widely used method. Atmospheric reduced crude from any primary distillation tower is mixed with liquid propane at a ratio of approximately 1:4 to 1:10 under a pressure of approximately 300 psig. Propane deasphalting has its limitations since it is used primarily for crude oil of relatively low asphalt content, generally less than or equal to 15%. Also, propane deasphalting has a very high capital investment cost, and again considering propane is a highly flammable and explosive gas at room temperature and atmospheric pressure and is used in extremely large quantities, the propane deasphalting process is also considered to be extremely risky.
Other residues such as the bottom products generated by used oil re-refineries using thin-film and wipe-film evaporators and petroleum sludges such as those from the storage tanks of crude oil, bunker C, slop oil, etc. are mostly disposed of through landfill and incineration. Alternatively, in particular, some residue of used oil re-refining plant is disposed of as flux of asphalt product. This means that the residue used is only a small fraction of the end product and therefore, do not significantly decrease the amount of sludge and residue in existence. The traditional disposal method of landfill and incineration has a number of drawbacks. For example, incineration of petroleum sludge or residue produces toxic gaseous emissions to the atmosphere. These emissions include sulphur and sulphur dioxide which are leading causes of acid rain which is causing great damage to Canadian, English, and Scottish forests. In addition, landfill of petroleum sludge or used oil residues is hazardous to health since their components can leach into the water table below.
Thus, there is a need to develop a process to refine and recover the petroleum sludge and residue rapidly, economically and safely.